This invention relates to a rotor structure for an axial flow elastic fluid-utilizing machine such as a turbine. In particular, it relates to coupling the radially-extending blades carried by the rotor spindle in a manner where the blades can be easily disassembled and the tips or ends of the blades protected.
A variety of blade structures for turbines and compressors are known and a variety of techniques for minimizing vibrative stresses in blade strutures have been developed.
A major cause of turbine blade failure is high amplitude vibration in one or more of the natural modes of a turbine group leading to high cyclical fatigue crack initiation and propogation, and in some cases, loss of a blade. Different blade designs to avoid problems of vibration at different frequencies have addressed some of the problems. Blading structures are either free-standing designs or grouped in short arcs or long arcs by shrouds. Generally, a continuously coupled structure provides a blade performance which is superior to short arc groups and free-standing designs.
Examples of different blade structures which are known are those in U.S. Pat. Nos. 3,279,751; 3,588,278; 3,417,964; 3,606,578; 3,702,221, and 4,386,887, and U.S. patent application Ser. No. 668,160, filed Nov. 5, 1984 and U.S. patent application Ser. No. 656,187, filed Oct. 1, 1984; and in the transaction of the ASME Journal of Engineering for Power, Volume 103, PP 522-531, July 1981, Long Arc Shrouding--A Reliability Improvement for Untuned Steam Turbine Blading, "Ortolano, Et Al". All these references are incorporated by reference herein.
Although the continuous coupled or tie arrangement is advantageous, over the short arc and free-standing designs, one notable drawback to many of the continuous tie arrangements is the inability to disassemble the row of blades for inspection or repairs. Also, where continuous ties or free-standing blades are reasonably easy to disassemble, another problem that exists is that there is no protection for the end or tip of the blade. In cases where the blades are longer the feature of tip protection is important to prevent strumming and to reduce tip losses.
In view of this, an object of the invention is to provide a rotor structure which has the advantage of a substantially continuously tied or coupled blading structure or permits for long arc groups in a manner to suppress tangential and axial modes of vibration and yet permit for the relatively easy disassembly of the blades and also reduced tip losses.